Rotating machinery, such as turbine in which wheels mounted on a shaft, require rotary seals in the region where the shaft passes through the pressure chamber that contains the turbine wheels. Such seals inhibit leakage of working fluid from the pressure chamber into the seal operating environment and then into the atmosphere. In addition, seals are also required in other machinery.
Seals for rotating machinery usually comprise a labyrinth seal followed by a mechanical seal. Labyrinth seals serve to restrict the rate of flow of working fluid and reduce its pressure toward atmospheric pressure, but not to prevent or contain the flow. Typically, labyrinth seals have many compartments positioned very close to the surface of the shaft for presenting to the working fluid in the pressure chamber a torturous path that serves to reduce pressure and inhibit, but not halt leakage. A mechanical seal, on the other hand, serves to contain the working fluid. The extent to which containment is achieved depends on the design of the seal and the nature of the working fluid involved.
When the working fluid is steam, some escape of the working fluid can be tolerated. Nevertheless, a shaft seal for the steam turbine is a critical item. It is even more critical when the working fluid is a hydrocarbon, such as pentane or isopentane, and the turbine operates as part of an organic Rankine cycle power plant. In such case, the mechanical seals must preclude to as great an extent possible the loss of working fluid to the atmosphere. Reliable operation of the mechanical seals for turbines, as well as for other types of equipment where the temperature of the mechanical seal is elevated, requires the seals to operate under optimum working conditions of pressure, temperature, vibration, etc. These working conditions have a significant impact on seal leakage rates and seal life expectancy, for example. By extending seal life, turbine life and hence reliability is extended.
Seal life is adversely affected by high operating pressure and temperature that tends to distort seal faces. High operating pressure also increases wear rate, heat generated at the seal faces which further distorts seal faces and results in increased leakage. In addition, the high pressure increases power consumption for the turbine sealing system.
In a related system, described in U.S. Pat. No. 5,743,094, the disclosure of which is incorporated by reference, a method of and apparatus for cooling a seal for machinery is disclosed. In the system and apparatus disclosed in the '094 patent, a cooled surroundings is produced in the seal operating environment in which a mixture of cooled liquid droplets and vapor is present. This mixture is supplied to the condenser of the power plant unit for condensing the vapor present in the mixture. Such a system, thus requires a condenser for condensing the cooled mixture present in the seal-operating environment.
High operating temperatures of the seal components adversely affect seal life. High seal component temperatures, increase wear on the seal faces, and also increase the likelihood that the barrier fluid when used will boil. It is therefore an object of the present invention to provide a new and improved method of and apparatus for cooling the seals for equipment.